Taking pain killers such as aspirin and paracetamol is not associated with an increased risk of damage to healthy kidneys, scientists say.

Doctors from the US monitored over 11,000 healthy men who used pain relief drugs over 14 years.

They found "no significant associations" between use of aspirin, paracetamol or other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen - and kidney damage.

But experts in the UK said there could be problems for some people who take the pain killers - particularly those who have a history of kidney problems.

Previous research had come to contradictory conclusions, with some suggesting analgesics, or pain relief drugs, were linked to increased risk of kidney damage, while others did not.

However, high doses of the drugs, particularly NSAIDs, have been implicated as causes of acute renal failure, which usually occurs in patients with impaired kidney function.

The scientists who carried out this research, published in the Journal of the American Medical Association, say it is the largest study to date.

They write: "This study provides reassuring evidence that there does not appear to be a strong association between chronic analgesic use and chronic renal dysfunction."

Creatinine levels

Men who were taking part received annual check-ups to monitor their health.

Their use of pain relief drugs was monitored, as were their levels of creatinine.

Creatinine is a waste-product of the body's processing of proteins.

People whose kidneys are not working properly have high levels of blood creatinine.

Scientists can check levels in the body and how quickly blood is cleared of the substance.

Only 4% of the men had higher than average creatinine levels and 11.5% had lower than average clearance.

The scientists, from Brigham and Women's Hospital, Boston, said there was no link between the use of the pain relief drugs and affects on creatinine levels or clearance - even amongst those men who had total intakes of 2,500 or more pills - which is an average of three to four per week.

They wrote: "While more research is needed, we believe these findings provide reassurance to clinicians and patients that moderate analgesic use is unlikely to contribute to an increased risk of renal dysfunction among individuals without a history of renal impairment."

Concern

But a spokesperson for the National Kidney Research Fund told BBC News Online some pain relief drugs, but not usually aspirin or paracetamol, could cause a relatively rare but potentially life threatening sudden allergic inflammation of the kidney.

She said there could also be a problem for patients who already have kidney problems who take large doses either over many years - or at once as a suicide attempt.

She added: "There is some anxiety that if large doses can cause disease in many subjects, lower doses may cause it in a few subjects.

"This study is reassuring on this point within its limitations."

The advice the fund gives is:

Don't take analgesics unless you really need them

Take single drugs such as an aspirin or paracetamol

Carefully study the instructions

If you have any kidney disease seek medical advice before taking analgesics